In Search of Lost Salmon-New Research Identifies Where they are From

A new technique for monitoring the spatial distribution of populations of marine animals is described in a paper published online in Scientific Reports. The work could help to identify areas in which the creation of marine reserves would be particularly valuable.

A primary method of studying the migrations of marine animals involves tagging the animals in a known location and then subsequently recapturing them elsewhere, either in research or commercial fisheries. But the high mortality and low recapture rates involved mean large numbers of animals must be tagged to provide meaningful results.

Using the Atlantic salmon (Salmo salar) as a test species, Kirsteen MacKenzie and colleagues report that the movements of marine populations can be monitored by analyzing the carbon isotope composition of these organisms. Carbon isotope composition of animal tissues varies with sea surface temperature, which means that the geographical position of individual salmon can be identified by comparing series of carbon isotopes measured in tissues with sea surface temperature records for the same time periods. The results allow the authors to identify feeding grounds used by individuals from different natal populations.

The technique, which can be applied retrospectively, could be used to study the spatial distribution of other marine species, such as tuna, herring and turtles, and could be useful in determining the influence of long-term climate change on these species.